Mac Pro RAM upgrade... not detecting original stock RAM now?

Discussion in 'Mac Pro' started by blarian, May 14, 2008.

  1. blarian macrumors newbie

    May 14, 2008
    I recently bought two 2GB sticks of OWC 800 MHz ram for my Mac Pro.

    My Mac Pro originally had two 1GB sticks, which worked fine, I just wanted more.

    It seems that they don't work together. I've tried every possibly configuration. Is it the case that they just aren't going to work together because they are different sizes?

    Right now, I have the two 2GB sticks in A1 and A2. And the stock 1GB sticks in B1 and B2. A1 and A2 gets detected, but B1 and B2 doesn't.
  2. Tattoo macrumors 6502

    Mar 30, 2005
    Miami, Florida
    Did you follow the instructions?
    I have the same set up as you. You take the original stick from card B and put it with the original stick on card A.

    You install the OWC memory both in card B.

    Works like a charm for me. Did you read what OWC put in the package?
  3. Tbarr macrumors member

    Mar 27, 2008
    Yep, that happened to me as well. Not the first time I installed it, but, when I tried to experiment to get more uniform temps. I had the 2x1GB in the upper card and the 2x2 in the lower card. After I switched them, the lower sticks were not recognized. I switched them a couple times, it was always the lower sticks that weren't seen.

    I fixed that by unplugging everything and waiting a couple minutes. See;
    I also found that the Lower memory runs hotter than the Upper... by about 20F. After placing the OWC 2x2GB in the Upper card, they are now reported as almost the same temp as the Apple 2x1GB in the Lower card. Now instead of around 120F on the Upper, and 140F on the Lower, they both read around 130F. I'm happy ;)
  4. demeni macrumors newbie

    Mar 3, 2008
    As the two RAM risers are linked to the two separate memory buses you need to install in balanced pairs (1x1Gb and 1x2Gb in your case in each riser). Also, as far as I'm aware the best policy is to match the modules so don't use 2x1Gb and 2x2Gb, use 6x1Gb (3/3) for best performance!
  5. Tbarr macrumors member

    Mar 27, 2008
    The manual says different. Matched pairs means 1 pair = 1GB + 1GB. Second pair = 2GB + 2GB. If you look at page 46 of the manual, it will have you placing the 2-1GB sticks in the Top Riser and the 2-2GB sticks in the Bottom Riser. In my case, that will have the Bottom 4GBs running 20F hotter than the 2GBs in the Top Riser. Swap it, and they both run the same temperature.


  6. darksun macrumors newbie

    Jul 2, 2008
    Got it working with 10GB!!!

    Thanks a ton guys.

    As Tattoo mentioned, I had not looked at the sheet provided by OWC

    My configuration is now as follows:

    Top Riser : 1: 2GB (OWC) 2:2GB (OWC) 3. 1 GB (Stock) 4. 1 GB (Stock)
    Bottom Riser: 1: 2GB (OWC) 2:2GB (OWC)

    I just hope all my Video processing times go down a lot with this. It better!
  7. robbo007 macrumors newbie


    Apr 7, 2005
    Valencia, Spain
    Hello all,
    I have a MAcPro from 2008 (MacPro3,1) and it came with 2x1GB RAM. I've purchased 2x1GB and its only detecting the new purchased RAM.

    Here's what I've tried.

    Riser A DIMM1: 1GB (original RAM) Riser A DIMM2: 1GB (original RAM)
    Riser B DIMM1: 1GB (new RAM) Riser B DIMM2: 1GB (new RAM)

    Only detects RAM in RISER B

    Riser A DIMM1: 1GB (new RAM) Riser A DIMM2: 1GB (new RAM)
    Riser B DIMM1: 1GB (original RAM) Riser B DIMM2: 1GB (original RAM)

    Only Detects RAM in Riser A

    I've reset the PRAM too. Nothing???

    Any ideas?


Share This Page